CN102410993B - Element measurement method based on laser-induced plasma emission spectral standardization - Google Patents

Abstract

The invention relates to an element measurement method based on laser-induced plasma emission spectral standardization, which is used for element concentration detection.The method comprises the following steps: firstly converting the strength of characteristic spectral lines to the standard plasma temperature and the density ratio of the number of ions to the number of atoms of elements to be measured; then after the strength of the characteristic spectral lines is converted to the standard plasma temperature and the standard density ratio of the number of the ions to the number of the atoms of the elements to be measured, using the sum of the strength of the characteristic spectral lines of the atoms and the ions of the elements to be measured to compensate the density fluctuation in the total particle number in plasma caused by the change in ablation mass; and finally establishing an equation among the concentration of the elements to be measured, the strength of the characteristic spectral lines after conversion and the strength sum of the characteristic spectral lines. When the measurement is performed on a sample with unknown components, the concentration of the elements to be measured can be obtained according to a calibration model by spectral standardization. As the calibration model considers the ablation mass and the impacts of the temperature and the density ratio of the number of the ions to the number of the atoms of the plasma on measurement signals, the fluctuation of the spectral strength caused by the fluctuation of physical parameters of the plasma is compensated and the measurement precision is greatly improved.

Description

Based on the standardized elements are contained method of laser induced plasma emission spectrum

Technical field

The present invention relates to a kind of elements are contained method.Specifically, the ultimate principle of method is induced with laser plasma spectrum technology (LIBS), and has used spectrum Standardization Act to carry out online quantitative test fast to measuring sample.

Background technology

In recent years, induced with laser plasma spectrum technology (be called for short LIBS) is owing to having high sensitivity, without sample pretreatment and realize the advantages such as multielement measurement, becomes a kind of new element analysis technology., because this technology repeatable accuracy is low, when measurement of species elemental composition, precision is not high, has limited the application of this technology in elements are contained.

Summary of the invention

The object of the invention is for current induced with laser plasma spectrum technology repeatable accuracy low, the not high shortcoming of precision when direct measurement of species composition, provide a kind of based on the standardized elements are contained method of spectrum, can in induced with laser plasma spectrum system, use, to solve this problem that technology repeatable accuracy is low, accuracy of measurement is not high.

Technical scheme of the present invention is:

A kind of based on the standardized elements are contained method of spectrum, it is characterized in that the method comprises the steps:

1) for a known calibration sample of each concentration of element, in blanket gas atmosphere, utilize laser induced plasma measuring system to detect the diverse location of sample surfaces, each position obtains the spectrum that a width comprises each element atom and ion characteristic spectral line, and asks for respectively atomic features line strength, ion characteristic line strength, plasma temperature, electron density and the element ion number to be measured of the element to be measured in calibration sample and the ratio of atomicity;

2) for one group of calibration sample that constituent content to be measured is different, repeating step 1);

3) ask for the mean value of all time plasma temperatures of measuring of one group of calibration sample, and the mean value of element ion number to be measured and the ratio of atomicity, and plasma temperature using the mean value of plasma temperature as standard, using the element ion number to be measured in calibration sample with the mean value of the ratio of atomicity as the number of ions of the standard of element to be measured and the ratio of atomicity;

4), by atomic features line strength of all time elements to be measured of measuring of one group of calibration sample, be folded to the plasma temperature of standard and the number of ions of the standard of element to be measured and the ratio of atomicity described in step 3); By ion characteristic line strength of all time elements to be measured of measuring of one group of calibration sample, be folded to the plasma temperature of standard and the number of ions of the standard of element to be measured and the ratio of atomicity described in step 3);

A. utilize formula (I) to be folded to the standard plasma temperature T described in step 3) atomic features line strength of element to be measured ₀the number of ions of standard and the ratio r of atomicity with element to be measured ₀,

$I_{\mathrm{ij}}^I(T_0,r_0)=I_{\mathrm{ij}}^I\frac{r+1}{r_0+1}\frac{U^I\left(T\right)\exp (-E_i/k{T}_0)}{U^I\left(T_0\right)\exp (-E_i/\mathrm{kT})}---\left(I\right)$

Subscript I represents the atom of surveyed element S, and subscript i and j represent respectively energy level and lower energy level; The intensity of the characteristic spectral line that I is, r is element ion atomic particle number density ratio to be measured, and U (T) is partition function, and E, T and k be temperature and the Boltzmann constant of representative element excited energy, plasma respectively;

B. for the ion characteristic spectral line of element to be measured, utilize formula (II) to be folded to the standard plasma temperature T described in step 3) ₀the number of ions of standard and the ratio r of atomicity with element to be measured ₀,

$I_{\mathrm{mn}}^{\mathrm{II}}(T_0,r_0)=I_{\mathrm{mn}}^{\mathrm{II}}\frac{r_0(r+1)}{r(r_0+1)}\frac{U^{\mathrm{II}}\left(T\right)\exp (-E_m/k{T}_0)}{U^{\mathrm{II}}\left(T_0\right)\exp (-E_m/\mathrm{kT})}---\left(\mathrm{II}\right)$

Subscript m and n represent respectively energy level and lower energy level; Subscript II represents the ion of surveyed element S;

5) ask for the standard plasma temperature T being folded to described in step 3) ₀with the standard ionomer number of element to be measured and the ratio r of atomicity ₀atomic features line strength and ion characteristic line strength sum of element to be measured, i.e. I _t(T ₀, r ₀);

6) utilize pantogen subcharacter spectral line to be measured or ion characteristic spectral line to set up the calibration curve equation of element to be measured;

A. for pantogen subcharacter spectral line to be measured, take concentration of element C to be measured as dependent variable, to be folded to standard plasma temperature and the number of ions of standard and atomic features line strength of the element to be measured of atomicity ratio for the treatment of secondary element

and the atom of element to be measured and ion characteristic line strength and I _t(T ₀, r ₀) be independent variable, carry out multiple linear regression analysis, obtain calibration curve equation:

$C=a_I{I}_{\mathrm{ij}}^I(T_0,r_0)+a_2{I}_T(T_0,r_0)+a_3---\left(\mathrm{III}\right)$

Wherein a ₁, a ₂, a ₃for regression coefficient;

B. for the ion characteristic spectral line of element to be measured, take concentration of element C to be measured as target, to be folded to ion characteristic line strength of ion atoms number density ratio of the temperature of standard plasma and the standard of element to be measured

and element atom to be measured and ion characteristic line strength and I _t(T ₀, r ₀) be variable, carry out multiple linear regression analysis, obtain calibration curve equation:

$C=b_1{I}_{\mathrm{mn}}^{\mathrm{II}}(T_0,r_0)+b_2{I}_T(T_0,r_0)+b_3---\left(\mathrm{IV}\right)$

Wherein b ₁, b ₂, b ₃for regression coefficient;

7) the concentration of element prediction to be measured in testing sample;

For a testing sample of each concentration of element the unknown, method according to step 1) detects, and asks for respectively atomic features line strength, ion characteristic line strength, plasma temperature, electron density and the element ion number to be measured of the element to be measured in testing sample and the ratio of atomicity;

A. for the atomic features spectral line of the element to be measured of testing sample, utilize induced with laser plasma spectrum system to measure atomic properties line strength of element to be measured

according to step 4), 5) spectrum is carried out to standardization, obtain the atomic features line strength after standardization

be folded to standard plasma temperature T ₀with the standard ionomer number of element to be measured and the ratio r of atomicity ₀the strong and ion characteristic line strength sum I of the atomic features spectral line of element to be measured _t(T ₀, r ₀), utilize calibration curve equation (III) to try to achieve the concentration of element to be measured;

B. for ion characteristic spectral line, utilize induced with laser plasma spectrum system to measure ion characteristic line strength of element to be measured

according to step 4), 5) spectrum is carried out to standardization, obtain the ion characteristic line strength after standardization be folded to standard plasma temperature T ₀with the standard ionomer number of element to be measured and the ratio r of atomicity ₀the strong and ion characteristic line strength sum I of the atomic features spectral line of element to be measured _t(T ₀, r ₀), utilize calibration curve equation (IV) to try to achieve the concentration of element to be measured;

8), for the testing sample in step 7), take multiple measurements and try to achieve respectively the concentration of element to be measured in different positions.

In technique scheme, the blanket gas described in step 1) comprises air, N ₂, CO ₂or inert gas.

In technique scheme, the method for asking for plasma temperature described in step 1) adopts Boltzmann method, Saha Boltzmann method or multielement Saha Boltzmann method; Step 2) described in the method for asking for plasma electron density adopt spectral line Stark broadening method.

The present invention has the following advantages and high-lighting effect: because spectrum standardized method can improve the precision of LIBS quantitative analysis significantly, first the present invention is folded to characteristic spectral line intensity the ratio of the ion source subnumber of the plasma temperature of standard and the standard of element to be measured, then utilize pantogen daughter ion characteristic spectral line intensity to be measured and the fluctuation that compensates the spectral signal causing due to ablation quality fluctuation, thereby eliminate LIBS measure in because the fluctuate measuring-signal that causes of plasma characteristic parameters fluctuates, both can realize the full elemental analysis of sample, can improve again measuring accuracy.It is easy that the present invention has analysis, can realize multielement and measure, consuming time few, and safe and reliable feature.The method can detect analytical element component content by real-time online, for industrial processes provide elemental composition real time data.

Accompanying drawing explanation

Fig. 1 is the structural principle schematic diagram of induced with laser plasma spectrum measurement mechanism in the present invention.

Fig. 2 is calibration and the prediction curve illustration of matching in the present invention.

Fig. 3 is the process flow diagram of measuring method of the present invention.

Embodiment

Below in conjunction with drawings and Examples, the present invention is further illustrated.

One provided by the invention, based on the standardized elements are contained method of spectrum, is characterized in that the method comprises the steps:

1) for a known calibration sample of each concentration of element, in blanket gas atmosphere, utilize laser induced plasma measuring system to detect the diverse location of sample surfaces, each position obtains the spectrum that a width comprises each element atom and ion characteristic spectral line, and asks for respectively atomic features line strength, ion characteristic line strength, plasma temperature, electron density and the element ion number to be measured of element to be measured and the ratio of atomicity;

2) for one group of calibration sample that constituent content to be measured is different, repeating step 1);

3) ask for the mean value of all time plasma temperatures of measuring of one group of calibration sample, and the mean value of element ion number to be measured and the ratio of atomicity, and plasma temperature using the mean value of plasma temperature as standard, using the number of ions of element to be measured with the mean value of the ratio of atomicity as the number of ions of the standard of element to be measured and the ratio of atomicity;

4), by atomic features line strength of all time elements to be measured of measuring of one group of calibration sample, be folded to the plasma temperature of standard and the number of ions of the standard of element to be measured and the ratio of atomicity described in step 3); By ion characteristic line strength of all time elements to be measured of measuring of one group of calibration sample, be folded to the plasma temperature of standard and the number of ions of the standard of element to be measured and the ratio of atomicity described in step 3);

Relation formula (1) between atomic features line strength and the plasma physics parameter of element to be measured,

$I_{\mathrm{ij}}^I={\mathrm{Fn}}_s\frac{n^I}{n^{\mathrm{II}}+n^I}\frac{g_i\exp (-E_i/\left(\mathrm{kT}\right))}{U^I\left(T\right)}{A}_{\mathrm{ij}}---\left(1\right)$

Wherein, subscript I and II represent respectively atom and the ion of surveyed element S, and subscript i and j represent respectively energy level and lower energy level; I is the intensity of the characteristic spectral line that receives of detector, and F represents instrument parameter, for definite experiment condition, is a constant; A, g, U (T), represents respectively transition probability, statistical weight, partition function, E, T, k, respectively temperature and the Boltzmann constant of representative element excited energy, plasma; n _s, n ⁱ, n ^iIrepresent respectively total population density of surveyed element, atomicity density and ion number density, for the typical LIBS ion characteristic spectrum that only has atom and primary ionization to be measured, so n _s=n ⁱ+ n ^iI; Wherein the ratio of ion atoms population density can calculate by following formula:

$r=r(T,n_e)=\frac{n^{\mathrm{II}}}{n^I}={\left(\frac{2\mathrm{\π}{m}_e\mathrm{kT}}{h^2}\right)}^{3/2}\frac{2}{n_e}\frac{U^{\mathrm{II}}\left(T\right)}{U^I\left(T\right)}\exp (-\frac{E_{\mathrm{ion}}-\mathrm{\ΔE}}{\mathrm{kT}})---\left(2\right)$

Wherein n _ebe the electron density of plasma, h is Planck's constant, E _ionbe the ionization energy of ground state atom, Δ E is that ionization energy reduces the factor;

Relation formula (3) between ion characteristic line strength and the plasma physics parameter of element to be measured,

$I_{\mathrm{mn}}^{\mathrm{II}}={\mathrm{Fn}}_s\frac{n^{\mathrm{II}}}{n^{\mathrm{II}}+n^I}\frac{g_m\exp (-E_m/\left(\mathrm{kT}\right))}{U^{\mathrm{II}}\left(T\right)}{A}_{\mathrm{mn}}---\left(3\right)$

A. utilize formula (4) to be folded to the standard plasma temperature T described in step 3) atomic features line strength of element to be measured ₀the number of ions of standard and the ratio r of atomicity with element to be measured ₀,

$I_{\mathrm{ij}}^I(T_0,r_0)=I_{\mathrm{ij}}^I\frac{r+1}{r_0+1}\frac{U^I\left(T\right)\exp (-E_i/k{T}_0)}{U^I\left(T_0\right)\exp (-E_i/\mathrm{kT})}---\left(4\right)$

Subscript I and II represent respectively atom and the ion of surveyed element S, and subscript i and j represent respectively energy level and lower energy level; The intensity of the characteristic spectral line that I is, r is the ratio of ion atoms population density, U (T) is partition function, E, T, k, respectively temperature and the Boltzmann constant of representative element excited energy, plasma;

B. for the ion characteristic spectral line of element to be measured, utilize formula (5) to be folded to the described standard plasma temperature T of step (4) ₀the number of ions of standard and the ratio r of atomicity with element to be measured ₀,

$I_{\mathrm{mn}}^{\mathrm{II}}(T_0,r_0)=I_{\mathrm{mn}}^{\mathrm{II}}\frac{r_0(r+1)}{r(r_0+1)}\frac{U^{\mathrm{II}}\left(T\right)\exp (-E_m/k{T}_0)}{U^{\mathrm{II}}\left(T_0\right)\exp (-E_m/\mathrm{kT})}---\left(5\right)$

5) ask for the standard plasma temperature T being folded to described in step 4) ₀the number of ions of standard and the ratio r of atomicity with element to be measured ₀the strong and ion characteristic line strength sum of the atomic features spectral line of element to be measured, i.e. I _t(T ₀, r ₀);

6) utilize atomic features spectral line or ion characteristic spectral line to set up the calibration curve equation of element to be measured;

A. for the atomic features spectral line of element to be measured, take concentration of element C to be measured as dependent variable, to be folded to the number of ions of standard and atomic features line strength of the element to be measured of atomicity ratio of standard plasma temperature and element to be measured

and the atom of element to be measured and ion characteristic line strength and I _t(T ₀, r ₀) be independent variable, carry out multiple linear regression analysis, obtain calibration curve equation (6):

$C=a_1{I}_{\mathrm{ij}}^I(T_0,r_0)+a_2{I}_T(T_0,r_0)+a_3---\left(6\right)$

Wherein a ₁, a ₂, a ₃for regression coefficient;

B. for the ion characteristic spectral line of element to be measured, take concentration of element C to be measured as target, to be folded to ion characteristic line strength of element to be measured of ion atoms number density ratio of the temperature of standard plasma and the element to be measured of standard

and element atom to be measured and ion characteristic line strength and I _t(T ₀, r ₀) be variable, carry out multiple linear regression analysis, obtain calibration curve equation (7):

$C=b_1{I}_{\mathrm{mn}}^{\mathrm{II}}(T_0,r_0)+b_2{I}_T(T_0,r_0)+b_3---\left(7\right)$

Wherein b ₁, b ₂, b ₃for regression coefficient;

7) concentration of element prediction to be measured;

For a testing sample of each concentration of element the unknown, in blanket gas atmosphere, utilize laser induced plasma measuring system to detect the diverse location of sample surfaces, each position obtains the spectrum that a width comprises each element atom and ion characteristic spectral line, and asks for respectively atomic features line strength, ion characteristic line strength, plasma temperature, electron density and the element ion number to be measured of element to be measured and the ratio of atomicity;

A. for atomic features spectral line, utilize induced with laser plasma spectrum system to measure atomic properties line strength of element to be measured

according to step 4), 5) spectrum is carried out to standardization, obtain the atomic features line strength after standardization

be folded to standard plasma temperature T ₀with the standard ionomer number of element to be measured and the ratio r of atomicity ₀the strong and ion characteristic line strength sum I of the atomic features spectral line of element to be measured _t(T ₀, r ₀), utilize calibration curve equation (6) to try to achieve the concentration C of element to be measured;

B. for ion characteristic spectral line, utilize induced with laser plasma spectrum system to measure ion characteristic line strength of element to be measured

according to step 4), 5) spectrum is carried out to standardization, obtain the ion characteristic line strength after standardization

be folded to standard plasma temperature T ₀with the standard ionomer number of element to be measured and the ratio r of atomicity ₀the strong and ion characteristic line strength sum I of the atomic features spectral line of element to be measured _t(T ₀, r ₀), utilize calibration curve equation (7) to try to achieve the concentration C of element to be measured;

8), for the testing sample in step 7), take multiple measurements and try to achieve respectively the concentration C of element to be measured in different positions.

Embodiment:

1) get 20 brass alloys that each concentration of element is known, as one group of calibration sample, number respectively 1 to 20, in this group sample, elemental copper concentration of element is respectively 73%, 60.28%, 59.14%, 56.62%, 59.55%, 69.08%, 80.9%, 85.06%, 90.02%, 95.9%, 96.86%, 94.46%, 92.7%, 89.97%, 70.44%, 67.59%, 64.32%, 63.42%, 60.81%, 57.98%.For each sample of 20 brass alloys, in blanket gas atmosphere, utilize laser induced plasma measuring system to detect the diverse location of sample surfaces, each position obtains the spectrum that a width comprises each element atom and ion characteristic spectral line, and asks for respectively atomic features line strength, ion characteristic line strength, plasma temperature, electron density and the element ion number to be measured of element to be measured and the ratio of atomicity;

2) mean value of trying to achieve all time plasma temperatures of measuring of 20 brass alloys is 9000K, and element ion number to be measured is 1.05 with the mean value of the ratio of atomicity, and plasma temperature using the mean value 9000K of plasma temperature as standard, using element ion number to be measured with the mean value 1.05 of the ratio of atomicity as the number of ions of the standard of element to be measured and the ratio of atomicity;

3), for atom and ion characteristic line strength of element Cu, be folded to ion and the atomicity density ratio of the plasma temperature of standard and the standard of element to be measured;

4) utilize following formula to be folded to the plasma temperature T of standard each characteristic spectral line intensity of surveyed element ₀ion and atomicity density ratio r with the standard of element to be measured ₀, atomic features spectral line is had,

$I_{\mathrm{ij}}^I(T_0,r_0)=I_{\mathrm{ij}}^I\frac{r+1}{r_0+1}\frac{U^I\left(T\right)\exp (-E_i/k{T}_0)}{U^I\left(T_0\right)\exp (-E_i/\mathrm{kT})}---\left(1\right)$

Each ion characteristic line strength of the element of surveying utilizes following formula to be folded to the plasma temperature T of standard ₀ion and atomicity density ratio r with the standard of element to be measured ₀,

$I_{\mathrm{mn}}^{\mathrm{II}}(T_0,r_0)=I_{\mathrm{mn}}^{\mathrm{II}}\frac{r_0(r+1)}{r(r_0+1)}\frac{U^{\mathrm{II}}\left(T\right)\exp (-E_m/k{T}_0)}{U^{\mathrm{II}}\left(T_0\right)\exp (-E_m/\mathrm{kT})}---\left(2\right)$

5) choose atom and the ion characteristic spectral line of the element to be measured that meets lorentzian curve, be respectively Cu (I) 216.51,261.837,282.437,296.116,427.511,522.007,570.024,578.213,793.312,809.263nm; Cu (II) 201.69,202.549,204.38,206.242,208.792,210.039,216.991,221.027,224.7,226.379,227.626,229.437,236.989,239.269,240.012,248.965,250.627,254.481,330.795,334.372,589.046,766.465nm, is folded to atom and ion characteristic line strength respectively ion and the atomicity density ratio of the plasma temperature of standard and the standard of element to be measured, then asks for to treat secondary element atom and ion characteristic line strength and I after amounting to _t(T ₀, r ₀); Be folded to element atom to be measured and ion characteristic line strength sum I of the ratio of the standard ionomer atomicity of standard temperature and element to be measured _t(T ₀, r ₀) change for compensating the total population of the plasma causing due to ablation mass change;

6) set up the calibration curve equation of element to be measured;

For ion characteristic spectral line Cu (II) 221.027nm, take element Cu concentration C as target, to be folded to the characteristic spectral line intensity of ion atoms number density ratio of standard of standard plasma temperature and element to be measured

and all atoms and ion characteristic line strength and I _t(T ₀, r ₀) be variable, carry out multiple linear regression, obtain calibration curve equation 3,

$C=b_1{I}_{\mathrm{mn}}^{\mathrm{II}}(T_0,r_0)+b_2{I}_T(T_0,r_0)+b_3---\left(3\right)$

Wherein b ₁, b ₂, b ₃for regression coefficient;

7) element Cu concentration prediction;

Take copper concentration as 79.1% brass alloys sample is as testing sample, sample is packed into measurement mechanism; In blanket gas atmosphere, utilize laser induced plasma measuring system to detect the diverse location of sample surfaces; Ask for the temperature of plasma, electron density and element ion to be measured and atomicity density ratio; Then, carry out standardization according to step 4,5 pairs of spectrum; Finally for ion characteristic spectral line Cu (II) 221.027nm, the characteristic spectral line intensity of ion atoms number density ratio of standard that is folded to standard plasma temperature and element to be measured

and all atoms and ion characteristic line strength and I _t(T ₀, r ₀) substitution calibration curve equation 3, obtain the element Cu concentration of this sample.For testing sample, repeat above-mentioned steps 10 times.Measurement result sees the following form.

Brass sample concentration prediction

8) measurement result is passed through Computer display.

The online detection instrument corresponding with said method comprises pulsed laser 1, condenser lens 2, gathers lens 3, optical fiber 4, CCD spectrometer 5, computing machine 6, it is characterized in that pulsed laser 1 is arranged on the top of condenser lens 2, condenser lens 2 is positioned at the top of the sample 3 on belt, and collection lens 4 are positioned at the side of sample.Sample 3 on belt passes through from condenser lens 2 bottoms.Gather lens 4 and be connected with the input section of spectrometer 6 by optical fiber 5, the output terminal of spectrometer 6 is connected with computing machine 7.

Principle of work of the present invention is:

Induced with laser plasma spectrum technology refers to that when intense pulse laser is irradiated on sample through focusing on, sample can be gasificated into high temperature, highdensity plasma in moment, and the plasma cognition in excited state externally discharges different rays.The wavelength that plasma emission spectroscopy spectral line is corresponding and intensity reflect respectively component and its concentration in surveyed object.This technology has high detection sensitivity, and cost is lower, can be simultaneously multiple element be analyzed etc. to advantage, the application potential that has huge element on-line analysis to detect.

In the repeatedly LIBS to same even sample measures, due to experiment parameter fluctuations such as laser energy, time delay, sampling gate-widths, one of shortcoming of LIBS is that repeatability precision is low.The present invention is the physical parameter ablation quality of plasma, the fluctuation of plasma temperature and electron density is considered in calibration model and is gone, thereby the relation between atomic features spectral line and elemental mass concentration is described more accurately, therefore fluctuation that can compensation experiment parameter, improves the precision of calibration model.

Under stoichiometric ablation (being concentration of element concentration of element in representative sample completely in plasma) and local thermodynamic equilibrium (LTE) assumed condition, the uncertainty of measuring-signal is mainly derived from ablation quality, plasma temperature, ion atoms is than the fluctuation of the physical characteristics parameters such as (electron number density) and plasma spatial form.First the method supposes plasma temperature and the atomic ion ratio of a standard; Then characteristic spectral line intensity is folded to the temperature of standard and the state of ion atoms ratio, changes thereby eliminate these two physical parameters the measuring-signal fluctuation causing; Because the characteristic spectral line intensity that is folded to uniform temp and ion atoms ratio is directly proportional to the total population of element to be measured, thus utilize be folded to uniform temp and ion atoms than many atoms and the fluctuation of line strength of causing due to ablation mass change of ion characteristic line strength and compensation.

What traditional single argument calibration model used is atomic spectral line or the ion line of element, uses the mode of regression fit to draw the relation of elemental mass concentration and line strength.This calibration process is to be based upon under the hypothesis that the ion atoms density ratio of identity element is constant.The atomic spectral line of wall scroll or ion line intensity basically can only representative element atomic concentration or ion concentration, and the direct total concentration of the total particle of representative element (atom+ion).Traditional single argument calibration model thinks that the concentration of ion or atom is into positive correlation with the total particle concentration of element, and this pass ties up in analytic process and remains unchanged.In practice, due to the variation of matrix effect and experiment parameter, the ratio of ion atoms is along with the variation of plasma physics parameter changes.So the hypothesis of traditional single argument calibration model can only could be set up in the time that the variation of plasma physics parameter can be ignored, this is one of important sources of univariate model error.The present invention derives a kind of standardized calibration model of spectrum of considering that plasma physics parameter changes theoretically, in the time that calculating, calibration considers the total population plasma temperature of element to be measured and electron density, and the impact of the ion atoms Density Ratio measuring-signal of identity element, thereby reach the fluctuation of compensation experiment parameter, improve the object of measuring accuracy.

Claims (3)

1. based on the standardized elements are contained method of laser induced plasma emission spectrum, it is characterized in that the method comprises the steps:

1) for a known calibration sample of each concentration of element, in blanket gas atmosphere, utilize laser induced plasma measuring system to detect the diverse location of sample surfaces, each position obtains the spectrum that a width comprises each element atom and ion characteristic spectral line, and asks for respectively atomic features line strength, ion characteristic line strength, plasma temperature, electron density and the element ion number to be measured of the element to be measured in calibration sample and the ratio of atomicity;

2) for one group of calibration sample that constituent content to be measured is different, repeating step 1);

3) ask for the mean value of all time plasma temperatures of measuring of one group of calibration sample, and the mean value of element ion number to be measured and the ratio of atomicity, and plasma temperature using the mean value of plasma temperature as standard, using the element ion number to be measured in calibration sample with the mean value of the ratio of atomicity as the number of ions of the standard of element to be measured and the ratio of atomicity;

4), by atomic features line strength of all time elements to be measured of measuring of one group of calibration sample, be folded to the plasma temperature of standard and the number of ions of the standard of element to be measured and the ratio of atomicity described in step 3); By ion characteristic line strength of all time elements to be measured of measuring of one group of calibration sample, be folded to the plasma temperature of standard and the number of ions of the standard of element to be measured and the ratio of atomicity described in step 3);

A. utilize formula (I) to be folded to standard plasma temperature described in step 3) and the number of ions of standard and the ratio of atomicity of element to be measured atomic features line strength of element to be measured,

$I_{\mathrm{ij}}^I(T_0,r_0)=I_{\mathrm{ij}}^I\frac{r+1}{r_0+1}\frac{U^I\left(T\right)\exp (-E_i/k{T}_0)}{U^I\left(T_0\right)\exp (-E_i/\mathrm{kT})}---\left(I\right)$

Subscript I represents the atom of surveyed element S, and subscript i and j represent respectively energy level and lower energy level; The intensity of the characteristic spectral line that I is, r is element ion atomic particle number density ratio to be measured, and U (T) is partition function, and E, T and k be temperature and the Boltzmann constant of representative element excited energy, plasma respectively; T ₀for standard plasma temperature, r ₀for the number of ions of standard and the ratio r of atomicity of element to be measured ₀;

B. for the ion characteristic spectral line of element to be measured, utilize formula (II) to be folded to standard plasma temperature described in step 3) and the number of ions of standard and the ratio of atomicity of element to be measured,

$I_{\mathrm{mn}}^{\mathrm{II}}(T_0,r_0)=I_{\mathrm{mn}}^{\mathrm{II}}\frac{r_0(r+1)}{r(r_0+1)}\frac{U^{\mathrm{II}}\left(T\right)\exp (-E_m/k{T}_0)}{U^{\mathrm{II}}\left(T_0\right)\exp (-E_m/\mathrm{kT})}---\left(\mathrm{II}\right)$

Wherein: subscript m and n represent respectively energy level and lower energy level; Subscript II represents the ion of surveyed element S; T ₀for standard plasma temperature, r ₀for the number of ions of standard and the ratio r of atomicity of element to be measured ₀;

5) ask for the standard plasma temperature T being folded to described in step 3) ₀with the standard ionomer number of element to be measured and the ratio r of atomicity ₀atomic features line strength and ion characteristic line strength sum of element to be measured, i.e. I _t(T ₀, r ₀);

6) utilize pantogen subcharacter spectral line to be measured or ion characteristic spectral line to set up the calibration curve equation of element to be measured;

A. for pantogen subcharacter spectral line to be measured, take concentration of element C to be measured as dependent variable, to be folded to standard plasma temperature and the number of ions of standard and atomic features line strength of the element to be measured of atomicity ratio for the treatment of secondary element

and the atom of element to be measured and ion characteristic line strength and I _t(T ₀, r ₀) be independent variable, carry out multiple linear regression analysis, obtain calibration curve equation:

$C=a_I{I}_{\mathrm{ij}}^I(T_0,r_0)+a_2{I}_T(T_0,r_0)+a_3---\left(\mathrm{III}\right)$

Wherein a ₁, a ₂, a ₃for regression coefficient;

B. for the ion characteristic spectral line of element to be measured, take concentration of element C to be measured as target, to be folded to ion characteristic line strength of ion atoms number density ratio of the temperature of standard plasma and the standard of element to be measured

and element atom to be measured and ion characteristic line strength and I _t(T ₀, r ₀) be variable, carry out multiple linear regression analysis, obtain calibration curve equation:

$C=b_1{I}_{\mathrm{mn}}^{\mathrm{II}}(T_0,r_0)+b_2{I}_T(T_0,r_0)+b_3---\left(\mathrm{IV}\right)$

Wherein b ₁, b ₂, b ₃for regression coefficient;

7) the concentration of element prediction to be measured in testing sample;

For a testing sample of each concentration of element the unknown, method according to step 1) detects, and asks for respectively atomic features line strength, ion characteristic line strength, plasma temperature, electron density and the element ion number to be measured of the element to be measured in testing sample and the ratio of atomicity;

Atomic features line strength and ion characteristic line strength according to step 4) to the element to be measured in testing sample are carried out standardization, obtain respectively the atomic features line strength after standardization

with the ion characteristic line strength after standardization ask for and be folded to standard plasma temperature T according to step 5) ₀with the standard ionomer number of element to be measured and the ratio r of atomicity ₀atomic features line strength and ion characteristic line strength sum I of element to be measured _t(T ₀, r ₀); Then utilize calibration curve equation (III) or (IV) try to achieve the concentration of element to be measured.

8), for the testing sample in step 7), take multiple measurements and try to achieve respectively the concentration of element to be measured in different positions.

2. according to claim 1 based on the standardized elements are contained method of laser induced plasma emission spectrum, be further characterized in that: the blanket gas described in step 1) comprises air, N ₂, CO ₂or inert gas.

3. according to claim 1 based on the standardized elements are contained method of laser induced plasma emission spectrum, be further characterized in that: the method for asking for plasma temperature described in step 1) adopts Boltzmann method, Saha Boltzmann method or multielement Saha Boltzmann method; The method of asking for electron density described in step 1) adopts spectral line Stark broadening method.

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